Here is the tutorial on programming smart key for Cadillac CT6 2016 under all keys lost situation by using
OBDSTAR X300 Pro3 Key Master auto key programmer.
Preparation: Two smart keys OBDSTAR X300 Pro3 key programmer Pin Code to car (get pin code by VPC-100 or other calculators)
Instruction: Connect OBDSTAR X300 Pro3 key programmer with vehicle Select Vehicles
Select Immobilizer Select GM Select GM V30.44
Select Immo/Remote function
Select vehicle make: Cadillac
Select CT6 Select Immobiliser
Select vehicle year: 2016
Select All keys lost Press start button once Put the smart key into the card slot,take other smart key out of the car,press ENTER to continue. The position of card slot is as follows: 1. In the armrests 2.Below the cup holder 3.Near the ashtray 4.Glove compartment
Switch igntion off Configuring the system,please wait
OBDSTAR Key Master require to enter 4-digit pin code Enter pin code and confirm Verifiy the security code Configuring the system,please wait for about 12 minutes
Erease success Press start button once X300 Pro3 prompt whether to program next key? Press ENTER to continue Remove key from card slot and out of car, and change another smart key, put the seconds key into the card slot Press start button once whether to program next key? Press ENTER, turn ignition OFF
Press start button for 12 sec Release start button and then press ENTER Press start button to swtich ignition on Switch ignition off
Press the brake and press the start button to start the engine Switch ignition off Remove smart key, press LOCK, and then press UNLOCK, press ENTER to continue Test new smart key is working
Program success!
Select Immobilizer Select GM Select GM V30.44 
Select Immo/Remote function 
Select vehicle make: Cadillac 
Select CT6 Select Immobiliser 
Select vehicle year: 2016 
Select All keys lost Press start button once Put the smart key into the card slot,take other smart key out of the car,press ENTER to continue. The position of card slot is as follows: 1. In the armrests 2.Below the cup holder 3.Near the ashtray 4.Glove compartment 
Switch igntion off Configuring the system,please wait 
OBDSTAR Key Master require to enter 4-digit pin code Enter pin code and confirm Verifiy the security code Configuring the system,please wait for about 12 minutes 
Erease success Press start button once X300 Pro3 prompt whether to program next key? Press ENTER to continue Remove key from card slot and out of car, and change another smart key, put the seconds key into the card slot Press start button once whether to program next key? Press ENTER, turn ignition OFF 
Press start button for 12 sec Release start button and then press ENTER Press start button to swtich ignition on Switch ignition off 
Press the brake and press the start button to start the engine Switch ignition off Remove smart key, press LOCK, and then press UNLOCK, press ENTER to continue Test new smart key is working 
Program success!